Conformational Study of Poly(γ-benzyl-L-glutamate) by Vibrational Circular Dichroism

Abstract

Poly(γ-benzyl-L-glutamate) (PBLG), a synthetic polypeptide, is soluble in organic solvents. Conformations and aggregation of PBLG were studied by vibrational circular dichroism spectroscopy (VCD) at various concentrations or acidities. In some solvents PBLG exhibits an α--helical conformation. The aggregation of PBLG was followed in CDCl₃, CHCl₃, C₆D₆ and C₆D₅NO₂. A decrease in aggregation was observed in 5 or 10 vol.% solutions of trifluoroacetic acid (TFA) in CHCl₃. The polyproline II conformation of PBLG was observed in 15 or 20 vol.% TFA solution in CHCl₃. In other solvents such as benzene, PBLG strongly aggregates; the formation of cholesteric liquid crystals was observed at concentrations higher than 50 g l⁻¹. These highly ordered structures were characterized by VCD signals that are about 100 times stronger than for PBLG in CDCl₃